Continuous variable transmission (CVT) is a user and environmentally friendly automatic type transmission that can be used in different industries as well as in transportation. In vehicles, the CVT causes automatic transmission by selecting the gear ratio that is the exact ratio needed for the road speed in which the vehicle is driven. Basically, the purpose of CVT is to continuously vary the transmission ratio. The idea of CVT is known for years; however, to date, its implementation in high power vehicles is cumbersome.
A number of different types of CVT have been developed in the past. Friction-based CVTs such as cone CVTs, transmit rotational movement between two wheels, at least one of which may vary in radius, using a transmission means such as a strap, which transfers the rotation by means of friction. Although easy in principle, the friction CVTs are incapable of transmitting the rotation at large torque or power because of the inherent slipping or skidding of the transmission means. Hydrostatic CVTs use a variable displacement pump and a hydraulic motor. All power is transmitted by hydraulic fluid. These types can generally transmit more torque, but can be sensitive to contamination. Some designs are also very expensive. A ratcheting CVT may vary the stroke of the reciprocating motion that is connected to a free wheel resulting in an unidirectional rotation. The drawback to ratcheting CVTs is undesired vibrations caused by the successive transition in speed required to accelerate an output shaft. Each mechanical system has its own inherent limitations.
At the early decades of the 20th century, one concept of the continuous transmission was developed by H. van Doorne. An experimental version was built in a Lloyd LP400 in the fifty's and eventually the first cars were ordered and produced by the DAF company. Although the technology of CVT actually dates back decades, these types of transmissions did not penetrate the car industry and has until recently been limited mostly to smaller cars with transversely-mounted engines and front wheel drive. Only in the recent years, there are attempts to drive the CVT into the mainstream of the automobile industry.
Other transmissions were developed and another example is the CLAAS′CVT. Primary components of the HM transmission of CLAAS are a reverse unit, hydrostatic unit, double planetary gear and low and high speed coupler shafts, and a multistep reduction gear downstream of the coupler shaft. The power is split in the reverse unit into mechanical and hydro static paths.
Audi's engineers developed a multitronic CVT for years and now stating that the multitronic finally overcomes all the drawbacks of the stepless principles. This CVT is an improvement of the van Doorne CVT type based on chain V-belt principle. A key element of the multitronic is a variator that adopts a new transmission element called a link-plate chain made entirely from steel and is almost as flexible as V-belt so to handle high forces and torque levels of the A6's engine. However, after few years of employing the multitronic in Audi cars, reports from customers show that after a certain amount of mileage, the multitronic is experiencing failure.
In general, the currently known CVT systems are not capable of handling high power and/or torque, such as the power and torque of trucks. Another drawback of the currently known CVT systems is the loss of engine power to the hydraulic side systems for clamping the driving belt on the pulleys or adapting the position of system components. Another source of power loss is the slip of the belts that occurs in these systems. A further problem may be the undesired vibrations which can occur, e.g. in ratcheting CVTs, due to e.g. stepwise moving components.
The current invention aims to deal with at least part of aforementioned drawbacks and provides an improved CVT, suitable for use with high power engines, and with minimized power loss to hydraulic side systems and which reduces slip. Additionally, the CVT of the invention optimizes fuel consumption, thereby lowering the average fuel consumption and thus provides an economic and ecological positive effect.